Apparatus for the measurement of the total content of organic carbon and nitrogen in water

ABSTRACT

The invention relates to a method for measuring of the total content of organic carbon and of nitrogen in water. The total organic carbon value is obtained correctly as the sum of the liquid, dissolved, and solid materials of a sample of the water. The device comprises a non-dispersive infrared (NDIR) gas analyzer for the simultaneous measurement of the concentration of the gas components carbon dioxide CO 2  and nitrogen oxide NO. The NDIR gas analyzer includes a phase separator (50), a thermal reactor (52), a double cooler (70), two valves (54, 56), as well as two amplifiers (58, 60) for the pneumatic signals of the receiver detectors (30, 36) with a display (62. 64) for the measured concentrations, total organic carbon and total nitrogen. The sample is split in a phase separator (50) into a gaseous and into a liquid part. The gaseous part, which comprises substantially the inorganic part of the carbon, the total inorganic carbon part in the form of carbon dioxide CO 2  gas, is cooled in a cooler to such an extent that a substantial part its water vapor content is deposited in the cooler by condensation. The dried gaseous part is led as comparison gas through the comparison cuvette. This step serves to compensate the total inorganic carbon part of the sample and to compensate for unavoidable water vapor cross-sensitivities during the measurement of the carbon dioxide CO 2  concentration and of the nitrogen oxide NO concentration.

This application is a divisional of Ser. No. 07/880,576 filed May 8,1992 now U.S. Pat. No. 5,292,666.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for the measurement of the totalcontent of organic carbon and of nitrogen in water, where a sample,taken from the water to be investigated and analyzed, is evaporated,wherein the organic carbon is oxidized to carbon dioxide, wherein thenitrogen is oxidized to nitrogen oxide in a thermal reactor, and whereinthe measurement is performed based on the gas sample, formed from thesample containing carbon dioxide CO₂ and nitrogen oxide NO.

2. Brief Description of the Background of the Invention Including PriorArt

The following abbreviations will be used in the following:

TOC=total organic carbon, indicating the total carbon present in thewater to be measured in the form of organic compounds.

TIC=total inorganic carbon, indicating the total carbon in the form ofinorganic compounds present in the water to be measured.

TC=total carbon, indicating the total carbon present in the water to bemeasured.

The organic part of carbon of the total organic carbon (TOC), is anoxygen consuming user and thus of interest in the determination of thechemical composition of waters. The German Industrial Standard 38 409(H) provides a basis for the determination of the total organic carbon(TOC) value.

The German Industrial Standard 38,409 (H) corresponds to the proposedInternational Standard ISO/DS 8245, submitted on Jan. 16, 1986 anddefines the designations TC=total carbon, TIC=total inorganic carbon andTOC=total organic carbon.

TN=total nitrogen, indicating the total amount of nitrogen present inthe water to be measured. The designation TN is defined in the proposedGerman Industrial Standard DIN 38,409, part 27.

Frequently, only a part, i.e., the part of the dissolved total organiccarbon (TOC) is captured in practical situations instead of the correctvalues. Frequently, also volatile organic components can be present inwater, which are lost during the separation of the sample of inorganiccompounds. Thus, the total organic carbon (TOC) value, is not completelycaptured with such a method.

The part of bonded nitrogen, total nitrogen (TN), is of interest inaddition to the total organic carbon (TOC) value. The total nitrogen(TN) value gives an indication relative to the load of the water withnitrogen compounds derived from natural and industrial discharges. Aproposal for the measurement of the total nitrogen (TN) is given in theproposed German Industrial Standard 38 409, part 27.

Total organic carbon (TOC) determinations are known. The total carbon(TC) and the total inorganic carbon (TIC) are measured and the totalorganic carbon (TOC) is determined by difference formation, compare forexample German Printed Patent documents DE-OS 2,811,135 (equivalent U.S.Pat. No. 4,217,108), DE-OS 2,458,143 (equivalent U.S. Pat. No.3,854,881), DE-OS 2,322,293 (equivalent U.S. Pat. No. 3,814,583), andEuropean Patent document EP-PS 0,150,923 (equivalent U.S. Pat. Nos.4,626,413, 4,666,860, 5,047,212).

A method for the continuous and quantitative determination of organicand inorganic carbon compounds in water is taught in the German PrintedPatent document DE-OS 3,909,240, wherein the water to be analyzed isacidified in a degasification vessel. A transport gas flow is fedthrough the water into the degasification vessel. Water and transportgas pass from the degasification vessel into a decomposition reactor.The carbon dioxide CO₂ content of the transport gas is determineddownstream of the degasification container or downstream of thedecomposition reactor. The parts of organic and inorganic carboncompounds are separated from each other or are determined as a sum.

F. Ehrenberger teaches in the paper entitled "For the determination ofthe oxygen requirement values and carbon characterizing values in thewater quality determination", GIT Fachz. Lab. 23, Voluble 8/79, pages738 through 747, several methods for the determination of total organiccarbon (TOC) , where the methods are based on wet chemical or thermalreaction of the organic content materials and on the quantitativeoxidation of the organically bonded carbon to carbon dioxide. The carbondioxide CO₂ content is determined by a chemical or physical method. Asimultaneous determination of nitrogen is not provided for in themethods described by F. Ehrenberger.

A value obtained by a total nitrogen (TN) auxiliary measurement is addedin individual cases to a value of a total organic carbon ( TOC )measurement by furnishing of a corresponding analyzer as set forth inthe German Printed Patent Document DE-OS 2,621,616 and in the equivalentU.S. Pat. No. 4,066,402. This method is expensive and generatesundesirable delay times of the display. Frequently, the calibration isperformed manually with a high-purity zero-conductivity water for thezero point establishment and with a calibration solution forestablishing the sensitivity. In addition, measurement errors caused bythe principle of the method are accepted. Thus, deviations from thepredetermined sensitivity occur if a base load of carbon dioxide CO₂becomes changed.

The German Printed Patent document DE-OS 2,621,616 to Yoshiki Komiyamateaches an analytical method and device for the determination of thetotal nitrogen and/or carbon contents in aqueous solutions which containnitrogen and/or carbon containing material.

The German Printed Patent document DE-OS 3,937,141 to Walter Fabinski,having an equivalent U.S. Pat. No. 5,055,688, teaches a non-dispersiveinfrared gas analyzer for the simultaneous measurement of theconcentration of several components of a gas sample. The NDIR gasanalyzer is suitable for the determination of the two gas components,carbon dioxide and nitrogen oxide. An analyzer is connected to andreceives signals from the receiver detectors. A control and display unitis connected to the analyzer.

The reference M. Ascherfeld et al. in "Technisches Messen--tm", Volume57/1990, Issue 1, pages 11-17, teaches "Expanded Possibilities andApplications with the NDIR Photometer Uras 10E".

The German Patent 2,105,307 to Theodor Bilichnianski teaches a liquiddispenser for feeding of reagents to an automatically operatingapparatus for the continuous analysis of samples.

The German Patent DE-3,640,718 C2 to Willi Apel et al. teaches amembrane capacitor for measuring of very small pneumatic alternatingpressures.

The German Printed Patent document DE-OS 3,909,240 A1 to Hans Duveteaches a method for the determination of disintegratable carboncompounds in water.

SUMMARY OF THE INVENTION

1. Purposes of the Invention

It is an object of the present invention to provide a method for thesimultaneous measurement of the total organic carbon (TOC) content andof the total nitrogen (TN) content in water, which captures thedissolved as well as the volatile components, which method considerszero point shiftings and sensitivity changes based on carbon dioxide CO₂changes during the total organic carbon (TOC) measurement as well ascross-sensitivities versus water vapor components during the totalnitrogen (TN) measurement, and which allows a zero point calibrationwithout using zero water.

It is another object of the present invention to provide a method whichallows an accurate and simultaneous determination of bound nitrogen andof organic bound carbon in a water-containing liquid.

It is yet another object of the present invention to furnish a methodfor the determination of organic bound carbon and for the determinationof bound nitrogen in water, which method is substantially automatic anddoes not require separate analytical methods.

These and other objects and advantages of the present invention willbecome evident from the description which follows,

2. Brief Description of the Invention

According to the present invention, there is provided for a method for adetermination of the total content of organic carbon and of nitrogen inan aqueous fluid sample comprising the following steps. An inorganiccarbon dioxide part is separated from a sample with the aid of a phaseseparator, wherein the inorganic dioxide part is loaded with watervapor. The inorganic carbon dioxide part is passed through a firstcooler. The inorganic carbon dioxide part coming from the first cooleris used as comparison gas. The inorganic carbon dioxide part is fed to acomparison cuvette. The inorganic carbon dioxide part coming from thecomparison cuvette is fed to a first input of a thermal reactor. Aremaining sample from the phase separator is fed to a second input ofthe thermal reactor. The carbon part present in the sample is oxidizedto carbon dioxide, and the nitrogen part present in the sample isoxidized to nitrogen oxide in the thermal reactor. The oxidized sampleobtained is loaded into a second cooler having the same temperature asthe first cooler. The oxidized sample is saturated with a water vapor ofa partial pressure corresponding to a water vapor saturation at the sametemperature as the temperature of water vapor saturation in thecomparison gas. The oxidized sample coming from the second cooler is fedas a measurement gas to a measurement cuvette. The measurement gascontains the total carbon dioxide part and the total nitrogen oxide partof the gas sample. The comparison cuvette and the measurement cuvetteare adjacently disposed cuvettes. The comparison gas with the actualinorganic carbon dioxide part is fed simultaneously through themeasurement cuvette and the comparison cuvette for taking intoconsideration the inorganic carbon dioxide CO₂ part, which is present asan interfering background in the sample. The measurement is performed onthe basis of the gas sample, containing carbon dioxide CO₂ and nitrogenoxide NO formed by the sample. A modulated light beam generated by aninfrared radiator is passed through the comparison cuvette and throughthe measurement cuvette. A light beam emanating from the comparisoncuvette is directed onto a first section of a first receiver detectordisposed behind the comparison cuvette. A light beam emanating from themeasurement cuvette is directed onto a second section of the firstreceiver detector disposed behind the measurement cuvette. A firstpneumatic signal is generated in the first receiver detector. Said firstpneumatic signal corresponds to the difference of the total carbon partand of the inorganic carbon part and thus corresponds to the organiccarbon part of the sample. The first pneumatic signal generated in thefirst receiver detector is amplified with a first electronic amplifier.The light beach emanating from the first receiver detector is filteredthrough a radiation filter disposed following the first receiverdetector. The radiation filter is transparent to the light beams in aregion of radiation absorption of the component nitrogen oxide NO of thesample. A second pneumatic signal is generated in a second receiverdetector sensitized to nitrogen oxide. The second receiver detectorexhibits two chambers. The two chambers in each case are filled with thesame gas component to be determined of the sample. The second pneumaticsignal generated in the second receiver detector is amplified with asecond electronic amplifier. Said second pneumatic signal corresponds tothe difference of the water vapor loaded nitrogen oxide part of themeasurement gas and of the water vapor part of the comparison gas andthus to the total nitrogen part of the sample.

A non-dispersive infrared gas analyzer can be employed for thesimultaneous measurement of the components carbon dioxide and nitrogenoxide in the sample. The inorganic carbon dioxide part coming from thecomparison cuvette can be fed to a first valve. The inorganic carbondioxide part from a first output of the first valve can be fed to afirst input of a thermal reactor. A liquid sample can be fed from thephase separator through a second input to the thermal reactor. The twochambers of the first receiver detector can be disposed successively asseen in beam direction.

A calibration cuvette having a first chamber filled can be furnishedwith a neutral gas in a path of the comparison beam and can have asecond chamber filled with a calibration gas in a path of themeasurement beam for setting the sensitivity of the gas analyzer for thegas components carbon dioxide CO₂ and nitrogen oxide NO to be measured.There can be set in a first step a zero point of the non-dispersiveinfrared gas analyzer for the total organic carbon value and the totalnitrogen value. The first chamber of the calibration cuvette can be slidinto a beam path between the first cuvette and the first receiverdetector, and the second chamber of the calibration cuvette can be slidbetween the second cuvette and the second receiver detector. Thesensitivity of the first amplifier can be set for the present inorganiccarbon dioxide concentration. The sensitivity of the second amplifiercan be set simultaneously with the setting of the sensitivity of thefirst amplifier for determining a nitrogen oxide concentration. Thecomparison gas can be fed to the comparison cuvette after termination ofthe setting processes for the zero point and for the sensitivity. Themeasurement gas can be fed to the measurement cuvette after terminationof the setting processes for the zero point and for the sensitivity.

The steps for the setting of the zero point and of the sensitivity ofthe gas analyzer can be repeated at predetermined time intervals for acontinuous consideration of the inorganic carbon dioxide part in thesample.

A connection to the measurement cuvette can be furnished in a returnline from the comparison cuvette to the thermal reactor such that thecomparison gas flows through the comparison cuvette and through themeasurement cuvette upon actuation of a first valve. A discharge of themeasurement gas from the reactor can be furnished in the feed line ofthe measurement gas to the measurement cuvette in front of or behind thedouble cooler upon actuation of a second valve. An actuation of thefirst valve and of the second valve can be performed during the settingof the zero point and of the sensitivity of the gas analyzer.

The measurement can be performed with a calibration liquid includingmaterials for total organic carbon and total nitrogen analysis as samplefor calibrating, wherein the following calibration steps are performed.The zero point and the sensitivity of the first amplifier and of thesecond amplifier can be set during the following above recited steps.The comparison gas with the actual inorganic carbon dioxide part can befed simultaneously through the measurement cuvette and the comparisoncuvette for taking into consideration the inorganic carbon dioxide CO₂part, which is present as an interfering background in the sample.According to a first step the zero point of the non-dispersive infraredgas analyzer for the total organic carbon value and the total nitrogenvalue can be set, and according to a second step, the calibrationcuvette can be slid into the beam path. The sensitivity of the firstamplifier can be set for the present inorganic carbon dioxideconcentration and simultaneously the sensitivity of the second amplifiercan be set for the nitrogen oxide concentration. The measurement gas canbe fed to the measurement chamber and the comparison gas can be fed tothe comparison chamber after termination of the setting processes forthe zero point and for the sensitivity. The first valve and the secondvalve can be deactivated and the sensitivity of the first amplifier andof the second amplifier can be set for the concentration values fortotal organic carbon and total nitrogen, predetermined by thecalibration liquid.

A sample of the water to be analyzed is fed to a phase separator, whichis frequently called stripper, where the sample is split up into agaseous and a liquid part. The gaseous part, which containssubstantially the inorganic part of carbon, which contains the totalinorganic carbon (TIC) part in the form of carbon dioxide CO₂ gas and inpart also carbon components in the form of easily volatile hydrocarboncompounds, is cooled in a cooler to a temperature of about 4° C. to suchan extent that a predominant part of a water vapor content present isdeposited in the cooler by condensation. The thus dried gaseous partpasses as a comparison gas into a comparison cuvette of a non-dispersiveinfrared (NDIR) gas analyzer operating according to the materialcomparison method. This step serves to compensate the total inorganiccarbon (TIC) part of the sample and to compensate the unavoidable watervapor cross-sensitivity during the measurement of the carbon dioxide CO₂concentrations and of the nitrogen oxide (NO) concentrations. Thegaseous part, exiting out of the comparison cuvette, is completelyreturned to the liquid part of the sample and is oxidized together withthe liquid part of the sample in a thermal reactor. The oxidation of thesample is performed both for the volatile part of carbon as well as forthe carbon part dissolved in water to give carbon dioxide CO₂ and forthe nitrogen part to give nitrogen oxide (NO).

The water vapor is separated from the thus obtained gas sample, whichgas sample contains the total carbon part and the total nitrogen part ofthe sample, in the cooler by condensation at the same temperature as thetemperature of the comparison gas and the gas sample is fed as ameasurement gas to the measurement cuvette of the NDIR gas analyzer. Apneumatic signal is generated in the first receiver sensitized to carbondioxide CO₂, where the pneumatic signal corresponds to the concentrationvalue of total carbon (TC) minus total inorganic carbon (TIC) and thusto the desired total organic carbon (TOC) value. A pneumatic signal isgenerated in the subsequently disposed receiver sensitized to nitrogen,where the pneumatic signal corresponds to the difference obtained fromthe water-vapor-loaded nitrogen oxide (NO) part of the measurement gasand of the water vapor part of the comparison gas, i.e., the desirednitrogen part (TN) in the sample.

The gas sample taken from the phase separator is led both through themeasurement channel as well as through the comparison channel forbalancing the zero point and the sensitivity of the analyzer. Zero pointshiftings of the amplifiers disposed downstream of the receivers, basedon carbon dioxide CO₂ offset changes or based on water H₂ O partscausing the cross-sensitivity, as well as aging and soiling of the gasanalyzer are balanced with this adjustment setting. Finally, the endpoint of the two amplifiers is set to the concentration values bysliding a calibration cuvette into the beach path between the cuvettesand the receivers, where the concentration values are predetermined bythe test gas enclosed in the calibration cuvette. This balancing methodassures that also small measurement regions can be realized withsufficient stability. In addition, this balancing method can beperformed based on gas stored in storage bottles and under eliminationof a requirement for use of external calibration gases.

The novel features which are considered as characteristic for theinvention are set forth in the appended claims. The invention itself,however, both as to its construction and its method of operation,together with additional objects and advantages thereof, will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a method for measuring the totalcontent of organic carbon and of nitrogen in water;

FIG. 2 shows a more detailed schematic diagram of a method for measuringthe total content of organic carbon and of nitrogen in water.

DESCRIPTION OF INVENTION AND PREFERRED EMBODIMENTS

The invention device includes a phase separator 50, a thermal reactor52, a double cooler 70 having a first cooler and a second cooler 76, twopaths 74, 76, and two valves 54 and 56.

A cooler can be provided by a conventional and commercially availablegas cooler. The reference paper GIT shows on page 743, in FIG. 11, anapparatus with a cooler, where the cooler is disposed downstream of athermal reactor.

The reference paper GIT describes on page 739, Section C, two methodsfor the separation of the total inorganic carbon TIC part out of anaqueous sample. The phase separator 50 of the present applicationoperates according to the degasification method described in thereference paper GIT. A phase separator can also be called a stripper ora sparger.

The reference German Printed Patent document DE-AS 2,260,295 and U.S.Pat. No. 3,703,355 show in FIG. 1 an evaporation chamber 12, whichoperates as a phase separator, wherein the inorganic carbon parts,present in a sample, such as carbonate, bicarbonate are transferred intocarbon dioxide CO₂ and are driven out from an aqueous sample by theaddition of inorganic acids.

The invention device comprises a known non-dispersive infrared (NDIR)gas analyzer for the simultaneous measurement of the concentration ofthe gas components carbon dioxide CO₂ and nitrogen oxide NO, with twoadjacently disposed cuvettes, the measurement cuvette 20 for themeasurement gas 22 and the comparison cuvette is 24 for the comparisongas 26. The measurement cuvette 20 and the comparison cuvette 24 arepassed by modulated light beams of an infrared radiator 28, wherein thelight beams fall onto pneumatic receiver detectors 30 and 36 afterpartial absorption in the measurement cuvette 20 and the comparisoncuvette 24 and in the calibration cuvette 44 . A chopper wheel 25 isdisposed between the infrared radiator source 28 and the comparisoncuvette 24 and the measurement cuvette 20 for providing lightmodulation. The receiver detectors 30 and 36 exhibit in each case twochambers 32, 34; 38, 40 disposed in series in beam direction, whereinthe two chambers 32, 34; 38, 40 in each case are filled with one of thecomponents to be determined of the gas sample and, in fact, the receiverdetector 30 with the component carbon dioxide CO₂ and the receiverdetector 36 with the component nitrogen dioxide NO.

A radiation filter 42 is disposed between the receiver detectors 30 and36. The radiation filter 42 is transparent to the light beams in theregion of the radiation absorption of the component nitrogen oxide NO ofthe gas sample. In addition, a calibration cuvette 44 with twoadjacently disposed chambers 46, 48 can be slid into the beam pathbetween the measurement cuvette 20 and the comparison cuvette 24 and thefirst receiver detector 30. The chambers 46, 48 of the calibrationcuvette 44 are filled with a calibration gas, for example, with carbondioxide CO₂ and/or nitrogen oxide NO in the measurement path and withnitrogen N₂, which is absorption neutral in the comparison beam path,for the adjustment setting of the sensitivity of the gas analyzer 82 forthe gas components carbon dioxide CO₂ and nitrogen oxide NO to bemeasured. The gas analyzer 82 includes the infrared radiator source 28,the comparison cuvette 24, the measurement cuvette 20, the calibrationcuvette 44; 46, 48 for the first receiver detector 30; 32, 34, theradiation filter 42, and the second receiver detector 36; 38, 40.

The construction and mode of operation of the employed gas analyzer 82,182, which serves for the quantitative and simultaneous determination ofcarbon dioxide CO₂ gas and nitrogen oxide NO gas is in general describedin the reference German Printed Published Patent document DE-OS3,937,141 and U.S. Pat. No. 5,055,688. Two separate light beams of theinfrared radiator 28 penetrate alternatingly the two cuvettes 20 and 24in their longitudinal direction and impinge subsequently onto thecalibration cuvette 44, onto the receiver detector 30 for carbon dioxideCO₂ gas, and onto the radiation filter 42, and the receiver detector 36for nitrogen oxide NO gas, in this sequence. For this purpose, thecuvettes passed through by the light beam are furnished with windowsopen in beam direction, where the windows are transparent to infraredradiation.

Two amplifiers 58 and 60 for the pneumatic signals received from thereceiver detectors 30 and 36 are connected to deliver amplified signalsto a display 62 for the measured concentrations total carbon (TC) minustotal inorganic carbon (TIC) and a display 64 for the measuredconcentrations total nitrogen (TN).

The chambers 32, 34; 38, 40 of the radiation receiver detectors 30 and36, disposed sequentially in beam direction, are filled with the gascarbon dioxide CO₂ or, respectively, nitrogen oxide NO to be determinedin each case. The gas volumes enclosed in the cheers 32, 34; 38, 40 arewarmed to varying degrees by absorption of the light beams penetratingthe chambers 32, 34; 38, 40. A higher pressure is generated in the frontchamber 32; 38 as compared to the rear chamber 34; 40 . The pressuredifference occurring is transformed into electric voltage variationswith the aid of a membrane capacitor 78, 80, where the membranecapacitor 78, 80 is indicated in FIG. 1 by the capacitor symbol, and ismeasured by a first electrical amplifier 58 or, respectively, by asecond electrical amplifier 60 and amplified. The output value ofcurrent or voltage of the amplifier 58, 60 is displayed with anelectrical display instrument 62, 64. The output value of the firstamplifier 58 or, respectively, of the second amplifier 60 is a measurefor the carbon dioxide CO₂ concentration or, respectively, of thenitrogen oxide NO concentration in the measurement gas 22.

An electrical display instrument 62, 64 is connected downstream of eachoutput of the amplifier 58, 60 for displaying the electrical outputvalue of the amplifier 58, 60, where the electrical output value of theamplifier 58, 60 represents a measure for the difference pressure signalof the respective receiver detectors 30, 36, as further indicated in theGerman Printed Patent document DE-OS 3,937,141, column 2, lines 54-58.

FIG. 2 shows a more detailed configuration of a second embodiment,configured similar to the embodiment of FIG. 1. The individualcomponents employed according to the FIG. 2 can be found in comparablesections described in connection with FIG. 1.

The apparatus for analyzing simultaneously organic carbon and nitrogenaccording to FIG. 2 comprises a phase separator 150 having an input, afirst output, and a second output. A first cooler 174 of a double cooler170 has an input connected to the first output of the phase separator150 and has a gas output. A first cuvette or comparison cuvette 124 hasa gas input connected to the gas output of the first cooler 174 and hasan output. A first valve 154 has an input connected to the output of thecomparison cuvette 124 and has a first output and a second output. Athermal reactor 152 has a first input connected to the first output ofthe first valve 154 and has a second input connected to the secondoutput of the phase separator 150 and has an output. A second cooler 176of the double cooler 170 has an input connected to the output of thethermal reactor 152 and has an output. A second valve 156 has an inputconnected to the output of the second cooler 176 and has a first outputand a second output. A second cuvette or measurement cuvette 120 has aninput connected to the output of the second valve 156 and has an output.An infrared radiator source 128 provides an infrared radiation to thefirst cuvette 124 and to the second cuvette 120. A chopper wheel 226 isdisposed between the infrared radiator source 128 and the comparisoncuvette 124 and the measurement cuvette 120. A calibration cuvette 144has a first chamber filled with a neutral gas, where the first chamberis disposed downstream of the comparison cuvette 124 in beam direction.The calibration cuvette has a second chamber filled with a calibrationgas, where the second chamber is disposed downstream of the measurementcuvette 120 in beam direction. A first receiver detector 130 is disposeddownstream of the calibration cuvette 144 in beam direction and has anoutput.

A radiation filter can be disposed following to the first receiverdetector in radiation direction and a second receiver detector can bedisposed following to the radiation filter in radiation direction andhaving an output. A first amplifier having an input connected to theoutput of the first receiver detector and having an output can beincorporated in the control display 208. A second amplifier having aninput connected to the output of the second receiver detector and havingan output can be incorporated in the control display 208. The controldisplay can include a first display having an input connected to theoutput of the first amplifier and a second display having the inputconnected to the output of the second amplifier.

A first control line 228 can provide a connection between the firstreceiver detector 130, the second receiver detector 136, and the controldisplay 208.

As shown in FIG. 2, a first connection is provided between the secondoutput of the first valve 154 and the input of the measurement cuvette120, and a second connection is provided between the output of themeasurement cuvette 120 and a second input of the second valve 156. Adischarge is located in the second connection.

A third valve 200 is connected to a sample probe source 202 and to azero probe source 204. A relay 206 of the third valve is connected by asecond control line 230 to the control display 208. A first membranepump 210 has a control input, an input, and an output. The input of thefirst membrane pump 210 is connected to the third valve 200. The controlinput of the first membrane pump 210 is connected by a third controlline 232 to the control display 208. A second membrane pump 212 has aninput connected to a source for acid 216 and has an output and a controlinput connected to a control output of the first membrane pump 210 andhas a control output. A separating column 218 has an input connected tothe output of the first membrane pump 210 and to the output of thesecond membrane pump 212 and an output connected to the phase separator150. A third membrane pump 214 has an input connected to the secondoutput of the phase separator 150 and has an output connected to aninput of the thermal reactor 152 and a control input connected to thecontrol output of the second membrane pump 212.

An air feed 220 is provided through the thermal reactor 152 having anair output. A first gas filter 114 has an input connected to the airoutput of the thermal reactor 152 and has an output connected to theinput of the separating column 218.

A first control connection 222 is furnished between the first valve 154and the control display 208 and a second control connection 224 isfurnished between the second valve 156 and the control display 208.

A second gas filter 110 is disposed between the output of the firstcooler 174 and the input of the first cuvette 124. A third gas filter112 is disposed between the output of the second cooler 176 and theinput of the second cuvette 120.

The mode of operation of the invention is as follows:

A sample of the water to be analyzed passes into the phase separator 50,wherein the phase separator 50 separates the inorganic carbon componentpart TIC from the sample, transforms and reacts this part into carbondioxide CO₂ gas, and feeds the carbon dioxide CO₂ gas via the line 66 tothe double cooler 70. The main amount of the water vapor is removed fromthe carbon dioxide CO₂ gas by condensation in the double cooler 70. Thecarbon dioxide CO₂ gas, thus dried at a temperature of about 4° C.,passes as a comparison gas C into the comparison cuvette 24. Then, thedried carbon dioxide gas passes through the comparison cuvette 24. Thedried carbon dioxide CO₂ gas passes from the comparison cuvette 24through the non-activated valve 54 into the thermal reactor 52.

If the connections of the three-way valves 54 and 56, respectively, aredesignated beginning in FIG. 1 at the left and going in a clockwisedirection with 1, 4 for <, 2, 5 for >, and with 3, 6 for , then theconnection 1-2 represents the gas path during non-activation of valve54.

If the valve 54 is activated, then a gas path exists from port 2 throughport 3. If the valve 56 is activated, then a gas path exists from port 4to port 6. The flow direction of the gases is indicated by the arrowdirection, indicated in the respective connection lines.

The dried carbon dioxide CO₂ gas is oxidized in the thermal reactor 52together with the liquid part of the sample, fed from the phaseseparator 50 via the line 68, to carbon dioxide CO₂ and nitrogen oxideNO.

A thermal reactor is described in the reference German Printed Patentdocument DE-OS 2,322,293 and U.S. Pat. No. 3,814,583 on page 4. Areaction vessel is shown, where continuously water is fed via line 1 tothe reaction vessel 2 and where air is fed via line 2 to the reactionvessel 2. The water is evaporated at a temperature of about 900° C. andthe carbon present in the water is oxidized with the oxygen present inthe air to carbon dioxide CO₂.

The gaseous oxidation product of the sample, designated in the followingas "the gas sample," contains the total carbon part and nitrogen part ofthe sample of the water to be analyzed. A substantial part of the watervapor is removed from the gas sample through condensation at the sametemperature of about 4° C. in the double cooler 70. The dried gas samplepasses through the non-activated valve 56 as a measurement gas 22 intothe measurement chamber 20 of a gas analyzer 82, 182.

Since the comparison gas 26 contains carbon dioxide CO₂, where theconcentration of the carbon dioxide CO₂ corresponds to the actualinorganic carbon component part TIC of the sample, there is generated inthe first receiver detector 30, sensitized to carbon dioxide CO₂, apneumatic signal.

The mode of operation of the pneumatic receiver detectors 30 and 36 isdescribed in more detail in the reference German Printed Patent documentDE-OS 3,937,141 and U.S. Pat. No. 5,055,688. The embodiment illustratedin FIG. 2 of the German Printed Patent document DE-OS 3937141 shows ananalyzer with two receiver detectors disposed in series in beamdirection. The first receiver is filled with carbon monoxide CO gas forthe determination of the carbon monoxide CO concentration of a gassample, and the rearward, second receiver is filled with carbon dioxideCO₂ gas and serves for the determination of the carbon dioxide CO₂concentration of the same gas sample. The generation of a differencepressure and the operation of transforming the difference pressure intoan electrical signal is performed with the aid of a membrane capacitorindicated in FIG. 1 by the capacitor symbol.

Said pneumatic signal corresponds to the difference of the concentrationvalue for the total carbon TC minus the concentration value for thetotal inorganic carbon TIC. This difference value, total carbon TC minustotal inorganic carbon TIC, is displayed through the amplifier 58 ondisplay 62. At the same time, a pneumatic signal is generated in thereceiver detector 36. The pneumatic signal of the receiver detector 36corresponds to the concentration value of the desired nitrogen part TN,displayed by amplifier 60 on display 64.

The cross-sensitivities versus water vapor, occurring during themeasurement of nitrogen oxide NO, can only be in part eliminated bycondensation of the gases in the upstream-disposed double cooler 70. Itis possible to set the measurement gas 20 and the comparison gas 26 tothe same low water vapor content by the step that the measurement gas 22and the comparison gas 26 are simultaneously led through the same doublecooler 70 and are cooled at the same temperature, such that thecross-sensitivities occurring in the measurement cuvette 20 and thecomparison cuvette 24 are compensated and balanced and the pneumaticsignals in the receiver detector 36 correspond to the undistorted anduncorrupted nitrogen oxide NO concentration value of the gas sample.

The zero point and the sensitivities of the measurement device aresubjected to various influences. Aging and water vaporcross-sensitivities of the gas analyzer 82, 182 as well as a sensitivityinfluence by the inorganic carbon dioxide CO₂ part, caused by themeasurement principle with a flowing comparison gas 26, belong to theseinfluences. The inorganic carbon dioxide CO₂ part can influence thesensitivity depending on the concentration up to several 100%. In orderto eliminate these influence effects , the measurement device isbalanced as follows sequentially after predetermined time intervals.

The following describes the adjustment of the measurement device.

The gas sample taken from the phase separator is fed through the gasline 66 and through the first cooler 74 of the double cooler 70 to thecomparison cuvette 24 and, upon activation of the valve 54 passing fromport 2 to port 3 of the valve 54, as well as by activation of the valve56 passing from port 4 to port 6, first toward the measurement cuvette20 and then to the discharge port 72. The downward arrow starting at themeasurement cuvette 20 of FIG. 1 represents the gas discharge port 72 .The gas discharge port can be a simple opening in a gas line, whichreleases the gaseous parts of the sample into the environment. The valve56 can also be disposed in front of the double cooler 70 such that thegas sample also passes over the second cooler 76 of the double cooler70. The influences changing the zero point are balanced with thisadjustment setting and with the aid of electronic means in theamplifiers 58 and 60. Then, the calibration cuvette 44 is slid into thebeam path between the measurement cuvette 20 and the comparison cuvette24 and the receiver detectors 30 and 36, and the sensitivity for thecarbon dioxide CO₂ channel and the nitrogen oxide NO channel is setcorresponding to the calibration gases disposed in the calibrationcuvette 44. The calibration cuvette 44 can contain carbon dioxide CO₂,nitrogen oxide NO, or a mixture of carbon dioxide CO₂ and nitrogen oxideNO. The calibration can be performed by a plurality of sequentialmeasurements with differently filled calibration cuvette 44. Thissetting takes also into consideration the influence of the actualinorganic carbon dioxide concentration in addition to apparatus agingand soiling, and correctly shows the total organic carbon content TOCvalue of the sample as sum of the volatile, dissolved and solidmaterials. It is an advantage that no zero liquid or calibration gas isrequired for this balancing step.

In addition to the above described method for the adjustment for themeasurement device, there is also to be performed a calibration of thetotal measurement device. In this case, modules such as pumps are alsotaken into consideration in the calibration of the total measurementdevice. This calibration is performed without a zero defining liquid.The calibration of the zero point and of the sensitivity is performedwith a calibration liquid fed to the phase separator 50, which containsa known concentration of organic carbon and of nitrogen compounds. Thecalibration liquid is fed as sample to the phase separator 50. Accordingto a first step, the zero point and the sensitivity of the device areset according to the above described adjustment based on the activationof the valves 54 and 56. According to a second step, these valves 54 and56 are deactivated. The receiver detectors 30 and 36 deliver in eachcase a pneumatic signal, which corresponds to the known concentration oforganic carbon and of nitrogen compounds. The sensitivity of thedownstream disposed amplifiers 58 and 60 are set with electronic meansbased on the thus generated signals. After termination of thecalibration process, the device is reset again to the measurementoperation for measuring the samples taken from the water to be analyzed.

A balancing process with the sample of the water, as described above,can follow immediately to the calibration of the measurement device inorder to establish the reference to the organic carbon dioxide CO₂content of the sample.

It is advantageous to perform the balancing process more frequently, forexample, every two to twelve hours, whereas the calibration process withthe calibration liquid should be performed, dependent on the measurementconditions, only every 2 to 24 days or repeated after even longer timeintervals.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofanalytical measurement devices and methods differing from the typesdescribed above.

While the invention has been illustrated and described as embodied inthe context of a method for the measurement of the total content oforganic carbon and nitrogen in water, it is not intended to be limitedto the details shown, since various modifications and structural changesmay be made without departing in any way from the spirit of the presentinvention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:
 1. An apparatus for the simultaneousanalysis of total content of organic carbon and nitrogen from an aqueoussample comprisinga phase separator having an input for receiving anaqueous sample, a first output, and a second output; a double coolerincluding a first cooler and a second cooler, wherein;the first coolerof the double cooler has an input connected to the first output of thephase separator and has a gas output; a first cuvette having a gas inputconnected to the gas output of the first cooler and having an output; afirst valve having an input connected to the output of the first cuvetteand having a first output and a second output; a thermal reactor havinga first input connected to the first output of the first valve andhaving a second input connected to the second output of the phaseseparator and having an output; wherein thesecond cooler of the doublecooler has an input connected to the output of the thermal reactor andhaving an output; a second valve having an input connected to the outputof the second cooler and having a first output, and a second output; asecond cuvette having an input connected to the first output of thesecond valve and having an output; an infrared radiator source providingan infrared radiation to the first cuvette and to the second cuvette; achopper wheel disposed between the infrared radiator source and thefirst cuvette and the second cuvette; a calibration cuvette having afirst chamber filled with a gas disposed after the first cuvette in beamdirection and having a second chamber filled with a calibration gasdisposed after the second cuvette in beam direction; a first receiverdetector disposed neighboring to the calibration cuvette in beamdirection and having an output; a radiation filter disposed following tothe first receiver detector in radiation direction; a second receiverdetector disposed neighboring to the radiation filter in radiationdirection and having an output; a first amplifier having an inputconnected to the output of the first receiver detector and having anoutput; a second amplifier having an input connected to the output ofthe second receiver detector and having an output; a first displayhaving an input connected to the output of the first amplifier anddisposed in a control display; a second display having the inputconnected to the output of the second amplifier and disposed in thecontrol display.
 2. The apparatus according to claim 1, furthercomprisinga first connection between the second output of the firstvalve and the input of the second cuvette; a second connection having adischarge and disposed between the output of the second cuvette and thesecond output of the second valve.
 3. The apparatus according to claim1, further comprisinga sample probe source; zero sample source; a thirdvalve connected to the sample probe source and connected to the zeroprobe source; a relay of the third valve connected by a second controlline to the control display; a first membrane pump having an inputconnected to the third valve and having an output, a control output anda control input; a third control line connecting the control input ofthe first membrane pump to the control display; a source for acid; asecond membrane pump having an input connected to the source for acidand having an output and having a control input connected to the controloutput of the first membrane pump and having a control output; aseparating column having an input connected to the output of the firstmembrane pump and to the output of the second membrane pump and havingan output connected to the phase separator; a third membrane pump havingan input connected to the second output of the phase separator andhaving an output connected to an input of the thermal reactor and havinga control input connected to the control output of the second membranepump.
 4. The apparatus according to claim 3, further comprisingan airfeed through the thermal reactor having an air output; a first gasfilter having an input connected to the air output of the thermalreactor and having an output connected to the input of the separatingcolumn.
 5. The apparatus according to claim 1, further comprisinga firstcontrol signal connection between the first valve and the controldisplay; a second control signal connection between the second valve andthe control display.
 6. The apparatus according to claim 1, furthercomprisinga second gas filter disposed between the output of the firstcooler and the input of the first cuvette; a third gas filter disposedbetween the output of the second cooler and the input of the secondcuvette.
 7. The apparatus according to claim 1, further comprisingafirst control line providing a connection between the first receiverdetector, the second receiver detector, and the control display.